Whole Exome Sequencing Reveals a Monogenic Cause of Disease in ≈43% of 35 Families With Midaortic Syndrome

Midaortic syndrome (MAS) is a rare cause of severe childhood hypertension characterized by narrowing of the abdominal aorta in children and is associated with extensive vascular disease. It may occur as part of a genetic syndrome, such as neurofibromatosis, or as consequence of a pathological inflammatory disease. However, most cases are considered idiopathic. We hypothesized that in a high percentage of these patients, a monogenic cause of disease may be detected by evaluating whole exome sequencing data for mutations in 1 of 38 candidate genes previously described to cause vasculopathy. We studied a cohort of 36 individuals from 35 different families with MAS by exome sequencing. In 15 of 35 families (42.9%), we detected likely causal dominant mutations. In 15 of 35 (42.9%) families with MAS, whole exome sequencing revealed a mutation in one of the genes previously associated with vascular disease (NF1, JAG1, ELN, GATA6, and RNF213). Ten of the 15 mutations have not previously been reported. This is the first report of ELN, RNF213, or GATA6 mutations in individuals with MAS. Mutations were detected in NF1 (6/15 families), JAG1 (4/15 families), ELN (3/15 families), and one family each for GATA6 and RNF213 Eight individuals had syndromic disease and 7 individuals had isolated MAS. Whole exome sequencing can provide conclusive molecular genetic diagnosis in a high fraction of individuals with syndromic or isolated MAS. Establishing an etiologic diagnosis may reveal genotype/phenotype correlations for MAS in the future and should, therefore, be performed routinely in MAS.

Clinical Trial of the Protein Farnesylation Inhibitors Lonafarnib, Pravastatin, and Zoledronic Acid in Children With Hutchinson-Gilford Progeria Syndrome

BACKGROUND

Hutchinson-Gilford progeria syndrome is an extremely rare, fatal, segmental premature aging syndrome caused by a mutation in LMNA yielding the farnesylated aberrant protein progerin. Without progerin-specific treatment, death occurs at an average age of 14.6 years from an accelerated atherosclerosis. A previous single-arm clinical trial demonstrated that the protein farnesyltransferase inhibitor lonafarnib ameliorates some aspects of cardiovascular and bone disease. This present trial sought to further improve disease by additionally inhibiting progerin prenylation.

METHODS

Thirty-seven participants with Hutchinson-Gilford progeria syndrome received pravastatin, zoledronic acid, and lonafarnib. This combination therapy was evaluated, in addition to descriptive comparisons with the prior lonafarnib monotherapy trial.

RESULTS

No participants withdrew because of side effects. Primary outcome success was predefined by improved per-patient rate of weight gain or carotid artery echodensity; 71.0% of participants succeeded (P<0.0001). Key cardiovascular and skeletal secondary variables were predefined. Secondary improvements included increased areal (P=0.001) and volumetric (P<0.001-0.006) bone mineral density and 1.5- to 1.8-fold increases in radial bone structure (P<0.001). Median carotid artery wall echodensity and carotid-femoral pulse wave velocity demonstrated no significant changes. Percentages of participants with carotid (5% to 50%; P=0.001) and femoral (0% to 12%; P=0.13) artery plaques and extraskeletal calcifications (34.4% to 65.6%; P=0.006) increased. Other than increased bone mineral density, no improvement rates exceeded those of the prior lonafarnib monotherapy treatment trial.

CONCLUSIONS

Comparisons with lonafarnib monotherapy treatment reveal additional bone mineral density benefit but likely no added cardiovascular benefit with the addition of pravastatin and zoledronic acid.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifiers: NCT00879034 and NCT00916747.

Nprl3 is required for normal development of the cardiovascular system

C16orf35 is a conserved and widely expressed gene lying adjacent to the human α-globin cluster in all vertebrate species. In-depth sequence analysis shows that C16orf35 (now called NPRL3) is an orthologue of the yeast gene Npr3 (nitrogen permease regulator 3) and, furthermore, is a paralogue of its protein partner Npr2. The yeast Npr2/3 dimeric protein complex senses amino acid starvation and appropriately adjusts cell metabolism via the TOR pathway. Here we have analysed a mouse model in which expression of Nprl3 has been abolished using homologous recombination. The predominant effect on RNA expression appears to involve genes that regulate protein synthesis and cell cycle, consistent with perturbation of the mTOR pathway. Embryos homozygous for this mutation die towards the end of gestation with a range of cardiovascular defects, including outflow tract abnormalities and ventriculoseptal defects consistent with previous observations, showing that perturbation of the mTOR pathway may affect development of the myocardium. NPRL3 is a candidate gene for harbouring mutations in individuals with developmental abnormalities of the cardiovascular system.

Mechanisms of premature vascular aging in children with Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome is a rare, segmental premature aging syndrome of accelerated atherosclerosis and early death from myocardial infarction or stroke. This study sought to establish comprehensive characterization of the fatal vasculopathy in Hutchinson-Gilford progeria syndrome and its relevance to normal aging. We performed cardiovascular assessments at a single clinical site on the largest prospectively studied cohort to date. Carotid-femoral pulse wave velocity was dramatically elevated (mean: 13.00±3.83 m/s). Carotid duplex ultrasound echobrightness, assessed in predefined tissue sites as a measure of arterial wall density, was significantly greater than age- and sex-matched controls in the intima-media (P<0.02), near adventitia (P<0.003), and deep adventitia (P<0.01), as was internal carotid artery mean flow velocity (P<0.0001). Ankle-brachial indices were abnormal in 78% of patients. Effective disease treatments may be heralded by normalizing trends of these noninvasive cardiovascular measures. The data demonstrate that, along with peripheral vascular occlusive disease, accelerated vascular stiffening is an early and pervasive mechanism of vascular disease in Hutchinson-Gilford progeria syndrome. There is considerable overlap with cardiovascular changes of normal aging, which reinforces the view that defining mechanisms of cardiovascular disease in Hutchinson-Gilford progeria syndrome provides a unique opportunity to isolate a subset of factors influencing cardiovascular disease in the general aging population.

Association of graft ischemic time with survival after heart transplant among children in the United States

BACKGROUND

Previous studies have found no association between graft ischemic time (IT) and survival in pediatric heart transplant (HTx) recipients. However, previous studies were small or analyzed risk only at the extremes of IT, where observations are few. We sought to determine whether graft IT is independently associated with graft survival in a large cohort of children with no a priori assumptions about where the risk threshold may lie.

METHODS

All children aged <18 years in the U.S. undergoing primary HTx (1987 to 2008) were included. The primary end point was graft loss (death or retransplant) within 6 months. Multivariate analysis was performed to analyze the association between graft IT and graft loss within 6 months after transplant. A secondary end point of longer-term graft loss was assessed among recipients who survived the first 6 months after transplant.

RESULTS

Of 4,716 pediatric HTxs performed, the median IT was 3.5 hours (interquartile range, 2.7-4.3 hours). Adjusted analysis showed that children with an IT > 3.5 hours were at increased risk of graft loss within 6 months after transplant (hazard ratio, 1.3; 95% confidence interval, 1.1-1.5; p = 0.002). Among 6-month survivors, IT was not associated with longer-term graft loss.

CONCLUSIONS

IT beyond 3.5 hours is associated with a 30% increase in risk of graft loss within 6 months in pediatric HT recipients. Although the magnitude of risk associated with IT is small compared with the risk associated with recipient factors, these findings may be important during donor assessment for high-risk transplant candidates.

Clinical, pathological, and molecular analyses of cardiovascular abnormalities in Costello syndrome: a Ras/MAPK pathway syndrome

Cardiovascular abnormalities are important features of Costello syndrome and other Ras/MAPK pathway syndromes ("RASopathies"). We conducted clinical, pathological and molecular analyses of 146 patients with an HRAS mutation including 61 enrolled in an ongoing longitudinal study and 85 from the literature. In our study, the most common (84%) HRAS mutation was p.G12S. A congenital heart defect (CHD) was present in 27 of 61 patients (44%), usually non-progressive valvar pulmonary stenosis. Hypertrophic cardiomyopathy (HCM), typically subaortic septal hypertrophy, was noted in 37 (61%), and 5 also had a CHD (14% of those with HCM). HCM was chronic or progressive in 14 (37%), stabilized in 10 (27%), and resolved in 5 (15%) patients with HCM; follow-up data was not available in 8 (22%). Atrial tachycardia occurred in 29 (48%). Valvar pulmonary stenosis rarely progressed and atrial septal defect was uncommon. Among those with HCM, the likelihood of progressing or remaining stable was similar (37%, 41% respectively). The observation of myocardial fiber disarray in 7 of 10 (70%) genotyped specimens with Costello syndrome is consistent with sarcomeric dysfunction. Multifocal atrial tachycardia may be distinctive for Costello syndrome. Potentially serious atrial tachycardia may present in the fetus, and may continue or worsen in about one-fourth of those with arrhythmia, but is generally self-limited in the remaining three-fourths of patients. Physicians should be aware of the potential for rapid development of severe HCM in infants with Costello syndrome, and the need for cardiovascular surveillance into adulthood as the natural history continues to be delineated.

Familial dilated cardiomyopathy secondary to dystrophin splice site mutation

BACKGROUND

Idiopathic dilated cardiomyopathy (DCM) encompasses a heterogeneous group of disorders, posing significant diagnostic challenges. Genetic etiologies underlie an important subset of DCM, including 20 genes and 5 X-linked disorders to date. We report a family with a rare dystrophin gene alteration, identified after evaluation of asymptomatic children whose extended family history included cardiomyopathy, premature cardiac death, or cardiac transplantation.

METHODS AND RESULTS

Record review, clinical evaluations, and DNA samples were obtained from members of a 5-generation pedigree with early onset DCM. Five of 6 affected males experienced death or cardiac transplant in their second or third decades. No affected individuals had skeletal muscle weakness before acute cardiac decompensation. Dystrophin gene analysis of an affected family member revealed sequence alteration at the conserved 5' splice site of exon 1 of the muscle-specific isoform of dystrophin (IVS1 +1 G>T) and co-segregated with cardiac disease in this family.

CONCLUSIONS

Young males presenting with apparent isolated cardiomyopathy or acute myocarditis may harbor dystrophin mutations without overt skeletal muscle pathology. The etiology of familial risk was not evident in this pedigree before retrospective cardiovascular genetics assessment, highlighting ongoing diagnostic challenges and limitations of standardized screening panels (which do not include dystrophin) in patients with "idiopathic" DCM.

Impact of ABO-incompatible listing on wait-list outcomes among infants listed for heart transplantation in the United States: a propensity analysis

BACKGROUND

The purported advantage of ABO-incompatible (ABO-I) listing is to reduce wait times and wait-list mortality among infants awaiting heart transplantation. We sought to describe recent trends in ABO-I listing for US infants and to determine the impact of ABO-I listing on wait times and wait-list mortality.

METHODS AND RESULTS

In this multicenter retrospective cohort study using Organ Procurement and Transplant Network data, infants<12 months of age listed for heart transplantation between 1999 and 2008 (n=1331) were analyzed. Infants listed for an ABO-I transplant were compared with a propensity score-matched cohort listed for an ABO-compatible transplant through the use of a Cox shared-frailty model. The primary end point was time to heart transplantation. The percentage of eligible infants listed for an ABO-I heart increased from 0% before 2002 to 53% in 2007 (P<0.001 for trend). Compared with infants listed exclusively for an ABO-compatible heart, infants with a primary ABO-I listing strategy (n=235) were more likely to be listed 1A, to have congenital heart disease and renal failure, and to require extracorporeal membrane oxygenation. For the propensity score-matched groups (n=197 matched pairs), there was no difference in wait-list mortality; however, infants with blood type O assigned an ABO-I listing strategy were more likely to undergo heart transplantation by 30 days (31% versus 16%; P=0.007) with a less pronounced effect for infants with other blood types.

CONCLUSIONS

The proportion of US infants listed for an ABO-I heart transplantation has risen dramatically in recent years but still appears to be preferentially used for sicker infant candidates. The ABO-I listing strategy is associated with a higher likelihood of transplantation within 30 days for infants with blood group O and may benefit a broader range of transplantation candidates.

Safety and early outcomes using a corticosteroid-avoidance immunosuppression protocol in pediatric heart transplant recipients

BACKGROUND

Long-term oral corticosteroids have been a mainstay of maintenance immunosuppression in pediatric heart transplantation. In this study, we report early clinical outcomes in a cohort of pediatric heart transplant recipients managed using a steroid-avoidance protocol.

METHODS

Of the 70 patients who underwent heart transplantation during the study period, 55 eligible recipients, including 49 non-sensitized and 6 sensitized (all 55 with negative crossmatch) patients, entered a steroid-avoidance immunosuppression protocol consisting of thymoglobin induction followed by a 2-drug, tacrolimus-based, corticosteroid-free regimen. The primary outcome variable was freedom from moderate rejection (International Society for Heart and Lung Transplantation [ISHLT] Grade 2R/3A or antibody-mediated rejection).

RESULTS

The median age at transplant was 7.1 years (range 2 weeks to 22 years) and median follow-up was 19 months (range 2 to 46 months). Fifty patients survived to discharge after transplantation. Of these patients, 2 (4%) were discharged on steroids and 8 (16%) started on maintenance steroids at follow-up. Rejection was diagnosed in 8 patients (Grade 2R cellular rejection in 3 and antibody-mediated rejection in 5). Freedom from rejection was 92% at 6 months (95% confidence interval [CI] 80% to 97%) and 87% at 1 year (CI 73% to 94%). Post-transplant survival was 91% at 6 months (CI 79% to 96%) and 88% at 12 and 24 months (CI 75% to 95%). There was 1 death due to rejection (antibody-mediated) 8 months after transplantation.

CONCLUSIONS

An immunosuppression protocol consisting of induction followed by corticosteroid avoidance appears to achieve acceptable rejection rates during the first year post-transplant in pediatric heart transplant recipients.

Clinical features of pulmonary arterial hypertension in young people with an ALK1 mutation and hereditary haemorrhagic telangiectasia

BACKGROUND

Pulmonary arterial hypertension (PAH) has been linked to mutations in genes encoding two members of the transforming growth factor-beta family, BMPR2 and ALK1, the latter of which is also associated with hereditary haemorrhagic telangiectasia (HHT). Relatively little is known about the genetics of childhood PAH, or about the clinical features of PAH in young patients with an ALK1 mutation.

METHODS AND RESULTS

Three individuals diagnosed with PAH at 4, 16 and 17 years of age were found on subsequent genetic screening to have non-synonymous mutations of ALK1. All probands met criteria for HHT, although two presented with PAH before HHT was diagnosed. Extended family history revealed relatives with HHT in all three kindreds, a presumptive family history of PAH in two, one with multiple family members dying from PAH at young ages. All three patients in this series had systemic or suprasystemic right ventricular pressure and significantly elevated pulmonary vascular resistance, initially not responsive to oxygen and/or inhaled nitric oxide. All patients had pulmonary arteriovenous malformations and systemic arterial desaturation.

CONCLUSION

This report highlights ALK1 mutations associated with a variable PAH phenotype, including pulmonary arteriovenous malformations and severe PAH presenting early in life. Echocardiographic screening for elevated right ventricular pressure may be indicated in patients with HHT, particularly those with an identified ALK1 mutation. Clinical features or a family history of HHT should be elicited in children and adolescents with idiopathic PAH; ALK1 screening may be appropriate when such features are present.

Spectrum of heart disease associated with murine and human GATA4 mutation

The transcription factor GATA4 is essential for heart morphogenesis. Heterozygous mutation of GATA4 causes familial septal defects. However, the phenotypic spectrum of heterozygous GATA4 mutation is not known. In this study, we defined the cardiac phenotypes that result from heterozygous mutation of murine Gata4. We then asked if GATA4 mutation occurs in humans with these forms of congenital heart disease (CHD). In mice, heterozygous Gata4 mutation was associated with atrial and ventricular septal defect (ASD, VSD), endocardial cushion defect (ECD), RV hypoplasia, and cardiomyopathy. Genetic background strongly influenced the expression of ECD and cardiomyopathy, indicating the presence of important genetic modifiers. In humans, non-synonymous GATA4 sequence variants were associated with ECD (2/43), ASD (1/8), and RV hypoplasia in the context of double inlet left ventricle (1/9), forms of CHD that overlapped with abnormalities seen in the mouse model. These variants were not found in at least 500 control chromosomes, and encode proteins with non-conservative amino acid substitutions at phylogenetically conserved positions, suggesting that they are disease-causing mutations. Cardiomyopathy was not associated with GATA4 mutation in humans. These data establish the phenotypic spectrum of heterozygous Gata4 mutation in mice, and suggest that heterozygous GATA4 mutation leads to partially overlapping phenotypes in humans. Additional studies will be required to determine the degree to which GATA4 mutation contributes to human CHD characterized by ECD or RV hypoplasia.

Cardiac Registry screening for DiGeorge Critical Region deletion using loss of heterozygosity analysis

DiGeorge (DGS), velocardiofacial, and conotruncal anomaly face syndromes comprise a phenotypic spectrum that is associated with a submicroscopic 22q11.2 deletion in the majority of cases. These syndromes variably express complex congenital heart disease, cellular immune deficits, hypocalcemia, craniofacial anomalies, and learning disabilities. This retrospective study correlates the presence of a deletion in this region with autopsy and clinical findings in a cohort of patients selected from the Cardiac Registry at Boston Children's Hospital. DNA was extracted from formalin-fixed paraffin-embedded cardiac tissue sampled from 189 patients with conotruncal anomalies. Polymerase chain reaction (PCR) was performed using 4 fluorescently labeled oligonucleotide primer pairs for unique short tandem repeat polymorphisms in the DGS critical region. The PCR products were analyzed for loss of heterozygosity (LOH), and a deletion was assumed when at least 3 consecutive loci demonstrated homozygosity. Of the 189 cases, 16 (8%) met our criteria for LOH and were assumed to have a deletion. These patients included 6 (35%) of 17 patients diagnosed clinically with DGS prior to death. Of the 10 non-DGS patients with LOH, 4 had aortic atresia and 3 had tetralogy of Fallot, both frequently seen in DGS. Polymerase chain reaction is a useful screening alternative to fluorescence in situ hydridization for detecting 22q11.2 deletions in archived tissue samples. This study identified a probable deletion in a subset of cases from a cardiac registry with cardiac defects associated with the DGS phenotype.

Connection between elastin haploinsufficiency and increased cell proliferation in patients with supravalvular aortic stenosis and Williams-Beuren syndrome

To elucidate the pathomechanism leading to obstructive vascular disease in patients with elastin deficiency, we compared both elastogenesis and proliferation rate of cultured aortic smooth-muscle cells (SMCs) and skin fibroblasts from five healthy control subjects, four patients with isolated supravalvular aortic stenosis (SVAS), and five patients with Williams-Beuren syndrome (WBS). Mutations were determined in each patient with SVAS and in each patient with WBS. Three mutations found in patients with SVAS were shown to result in null alleles. RNA blot hybridization, immunostaining, and metabolic labeling experiments demonstrated that SVAS cells and WBS cells have reduced elastin mRNA levels and that they consequently deposit low amounts of insoluble elastin. Although SVAS cells laid down approximately 50% of the elastin made by normal cells, WBS cells deposited only 15% of the elastin made by normal cells. The observed difference in elastin-gene expression was not caused by a difference in the stability of elastin mRNA in SVAS cells compared with WBS cells, but it did indicate that gene-interaction effects may contribute to the complex phenotype observed in patients with WBS. Abnormally low levels of elastin deposition in SVAS cells and in WBS cells were found to coincide with an increase in proliferation rate, which could be reversed by addition of exogenous insoluble elastin. We conclude that insoluble elastin is an important regulator of cellular proliferation. Thus, the reduced net deposition of insoluble elastin in arterial walls of patients with either SVAS or WBS leads to the increased proliferation of arterial SMCs. This results in the formation of multilayer thickening of the tunica media of large arteries and, consequently, in the development of hyperplastic intimal lesions leading to segmental arterial occlusion.

Elastin gene deletions in Williams syndrome

Williams syndrome is a developmental disorder affecting predominantly connective tissue and the central nervous system. Identification of elastin mutations in families with supravalvar aortic stenosis has enabled the identification of potentially large deletions that include one elastin allele in individuals with Williams syndrome. Current efforts are aimed at defining the extent of these deletions and additional genes that contribute to the Williams syndrome phenotype.

A fourth human MEF2 transcription factor, hMEF2D, is an early marker of the myogenic lineage

The transition from multipotent mesodermal precursor to committed myoblast and its differentiation into a mature myocyte involve molecular events that enable the cell to activate muscle-specific genes. Among the participants in this process is the myocyte-specific enhancer factor 2 (MEF2) family of tissue-restricted transcription factors. These factors, which share a highly conserved DNA-binding domain including a MADS box, are essential for the expression of multiple muscle genes with cognate target MEF2 sites in cis. We report here a new human MEF2 factor, hMEF2D, which is unique among the members of this family in that it is present not only in myotubes but also in undifferentiated myoblasts, even before the appearance of myogenin. hMEF2D comprises several alternatively spliced products of a single gene, one of which is the human homolog of the Xenopus SRF-related factor SL-1. Like its relatives, cloned hMEF2D is capable of activating transcription via sequence-specific binding to the MEF2 site, recapitulating endogenous tissue-specific MEF2 activity. Indeed, while MEF2D mRNAs are ubiquitous, the protein is highly restricted to those cell types that contain this activity, implicating posttranscriptional mechanisms in the regulation of MEF2D expression. Alternative splicing may be important in this process: two alternative MEF2D domains, at least one of which is specifically included during myogenic differentiation, also correlate precisely with endogenous MEF2 activity. These findings provide compelling evidence that MEF2D is an integral link in the regulatory network for muscle gene expression. Its presence in undifferentiated myoblasts further suggests that it may be a mediator of commitment in the myogenic lineage.

Human myocyte-specific enhancer factor 2 comprises a group of tissue-restricted MADS box transcription factors

The MEF2 site is an essential element of muscle enhancers and promoters that is bound by a nuclear activity found, so far, only in muscle and required for tissue-specific transcription. We have cloned a group of transcription factors from human muscle that are responsible for this activity: They are present in muscle-specific DNA-binding complexes, have a target sequence specificity identical to that of the endogenous activity, and are MEF2 site-dependent transcriptional activators. These MEF2 proteins comprise several alternatively spliced isoforms from one gene and a related factor encoded by a second gene. All share a conserved amino-terminal DNA-binding domain that includes the MADS homology. MEF2 transcripts are ubiquitous but accumulate preferentially in skeletal muscle, heart, and brain. Specific alternatively spliced isoforms are restricted to these tissues, correlating exactly with the presence of endogenous MEF2 activity. Furthermore, MEF2 protein is detected only in skeletal and cardiac muscle nuclei and not in myoblast and nonmuscle cells. Thus, post-transcriptional regulation is important in the generation of tissue-specific MEF2 activity. Cardiac and smooth, as well as skeletal, muscles contain functionally saturating levels of MEF2 trans-activating factors that are absent in nonmuscle cells. Moreover, MEF2 is induced in nonmuscle cells by MyoD; however, MEF2 alone is insufficient to produce the full muscle phenotype. Implications for the molecular mechanisms of myogenesis are considered.